Grassland expansions promoted global diversification of the Pardosa wolf spiders during the late Cenozoic (Araneae, Lycosidae)

The spiders in the genus Pardosa C.L. Koch, 1847, are a young lineage of the family Lycosidae Sundevall, 1833, that exhibit high species diversity and widespread distribution. Pardosa is abundant in open and disturbed environments. In fact, most of its species live in grasslands, and the few that live in forests switched habitats relatively recently. The genus markedly prefers grasslands with a broad range of climates. Thus, its origin and diversification were probably associated with grassland expansions during the late Cenozoic. To test this hypothesis, we developed a global phylogenetic hypothesis that helps reconstruct the biogeographic patterns of the genus Pardosa using three nuclear (18S, ITS2, and H3) and four mitochondrial (12S, 16S, NADH1, and COI) loci. Our phylogenetic analyses cover 133 (125 described and 8 as yet undescribed) grassland species of Pardosa using Trochosa ruricola (De Geer, 1778) and Lycosa coelestis L. Koch, 1878, as outgroups. The results show that our selection of species in the genus is divided into four major clades: Clade I includes only P. crassipalpis Purcell, 1903, from South Africa; Clade II consists of a north-east African group (2 species) and a south-east Asian group (21 species); Clade III contains only P. sutherlandi (Gravely, 1924) from SE Asia; and Clade IV includes five species groups from Asia, Europe, and the Americas. The spiders of the genus probably originated in southern Africa or southern and eastern (SE) Asia at the Middle Miocene Climatic Optimum, about 19.40–14.18 Ma, and then expanded northwards to North America via the Bering Strait, as well as southwards to north-east Africa via the Arabian Peninsula, and westwards to Europe via western Asia between about 10.59 and 5.28 Ma. At least three exchanges occurred between North America and SE Asia, and at least two between Europe and North America. The biogeography of Pardosa in the past 14.18 Ma, associated with the evolution of grasses, suggested a late Cenozoic diversification of the genus as grasslands expanded.